A thermal print head thus far known includes a substrate, a glaze layer, a heating resistor, and an electrode. Such a thermal print head is disclosed, for example, in Patent Document 1. In the thermal print head according to the document, the glaze layer is formed on the substrate. The glaze layer serves to accumulate heat generated in the heating resistor. The heating resistor is formed on the glaze layer. The heating resistor includes a plurality of heating portions. The heating portions are each spanned between two portions of the electrode spaced from each other. The cover layer is formed of glass for example, so as to cover both of the two portions of the electrode, and also the heating portion spanned between the two portions.
In the thermal print head configured as above, the heat generated by the heating portion may be transmitted through the glaze layer to a region in the glaze layer where another heating portion, adjacent to the first mentioned heating portion, is located. In such a case, an image printed on a printing medium may be blurred.
In the mentioned thermal print head, when the glaze layer is thin the glaze layer is unable to accumulate a sufficient amount of heat out of the heat generated by the heating portion. In this case the image may not be clearly printed on the printing medium. Accordingly, it has been a common approach to form a thicker glaze layer in order to obtain a clear image on the printing medium. However, a high-level technique is required to increase the thickness of the glaze layer.
In addition, when a considerable part of the heat transmitted from the heating portion to the glaze layer escapes to the substrate, a clear image may not be obtained on the printing medium.
With the mentioned thermal print head, the heat generated by the heating portion is transmitted to the printing medium through the cover layer. However, a part of the heat generated by the heating portion is transmitted to the glaze layer, and besides the heat diffuses while being transmitted through the cover layer. Accordingly, it is difficult to efficiently transmit the heat to the printing medium, and therefore the heating portion has to be configured to generate a larger amount of heat. To increase the amount of heat generated by the heating portion, a larger power has to be supplied to the electrode, which constitutes an obstacle against reduction of power consumption in the printing operation.